They are 它们就是

312. but they've also allowed a more infamous group of fish to rule the waves.
     但也使另一种更恶名昭彰的鱼类 统治海洋
313. They first appeared more than 400 million years ago
     它们最早出现在四亿多年前
314. and have been feared ever since.
     自那以来 一直威名显赫
315. They are
     它们就是
316. the sharks.
     鲨鱼
317. To the winning combination of backbone and jaws,
     在脊椎与颌的胜利组合之外
318. they've added senses so sharp
     它们还加入了异常敏锐的感官

来自《我们星球上的生命 第一季 第二集 Life on Our Planet S01E02 第一前线》第 315 行